Graded lithographic mask

ABSTRACT

In one aspect there is provided a gray scale lithographic mask that comprises a transparent substrate and a metallic layer located over the substrate, wherein the metallic layer has tapered edges with a graded transparency. The lithographic mask, along with etching processes may be used to transfer a pattern  450   a  into a layer of a semiconductor device.

TECHNICAL FIELD OF THE INVENTION

The invention is directed to a graded lithographic mask, a method of manufacturing that mask, and a method of using the mask to fabricate a semiconductor device.

BACKGROUND OF THE INVENTION

In the manufacture of semiconductor integrated circuit (IC) devices, a technique known as lithography is used for transferring ultra small circuitry patterns onto a semiconductor wafer. The lithograph technique typically includes a projection exposure apparatus, which loads a photomask and transfers the patterns located on the photomask onto a semiconductor wafer to expose portions of a photosensitive material located on the wafer. These patterns ultimately result in component structures e.g., transistors, capacitors, diodes, micro-electrical mechanical system (MEMS) devices, heating elements, optoelectrical devices, etc. Since the exposure area of the photomask is smaller in size than the area of the wafer, a wafer surface is typically divided into a plurality of “shots” that are conducted in a stepping fashion across the wafer.

Depending on the type and size of structures that are to be fabricated, different types of photomasks can be used. For example, the photomask may be a binary mask, a gray scale mask, or a phase shift mask. Binary masks typically consist of a quartz substrate with a patterned chromium layer located over it. This mask has been used extensively over the years in fabricating semiconductor devices. A gray scale mask can be used where a slope or stepped configuration needs to be incorporated into a layer of a device component or structure. In such instances, the chromium layer can be patterned from progressively smaller to lager exposure areas, which effectively form the slope or stepped edge configuration in the targeted wafer substrate or layer during a plasma etch.

In recent years, however, device patterns have been made progressively smaller and denser to meet the demand for higher performance devices. To achieve the reduced feature sizes, manufacturers have had to turn to using much smaller and denser patterns on photomasks. Consequently, shorter wavelengths are needed to properly expose these patterns onto an underlying photosensitive material.

As an alternative to previous photomasks and to accommodate the shorter wavelengths, phase shift masks have been developed. The phase shift mask is a mask having a translucent film formed on a transparent plate for attenuating the exposing light and shifting the phase. Typically, the transmission of the exposure light through the film is desirable in the range between approximately 1% and 40%. The light transmitted through this film is adjusted to have certain phase differences from the light that does not pass through the film. The best phase difference for achieving the highest resolution is at about 180° and odd multiples thereof. However, the resolution can be improved when the phase is approximately 180°±0.90°. When using a phase shift mask, the resolution may be improved by approximately 5% to 20%, thereby providing manufactures with the ability to manufacturer smaller and denser device components.

These binary, gray scale, and phase shift masks have been found to work well in fabricating different types of devices.

SUMMARY OF THE INVENTION

One aspect of the invention provides a method of manufacturing a semiconductor device. In this embodiment, the method comprises placing a mask layer over a layer that is located over a semiconductor substrate. A lithographic mask is used to expose the mask layer. The lithographic mask includes a mask substrate having a metallic layer located thereover, and the metallic layer has tapered edges wherein the tapered edges have a graded translucency. This embodiment further includes patterning the mask layer including forming tapered edges on the mask layer and etching the layer through the patterned mask layer to form a layer having tapered edges.

Another embodiment provides a gray scale lithographic mask that comprises a transparent substrate and a metallic layer located over the substrate, wherein the metallic layer has tapered edges with a graded transparency.

Yet another embodiment provides a method of fabricating a gray scale lithographic mask. This embodiment includes providing a transparent substrate, placing a metallic layer over the transparent substrate, forming a patterned etch mask over the metallic layer to expose portions of the metallic layer, and etching the exposed portions of the metallic layer to form tapered edges on the metallic layer wherein the tapered edges have a graded transparency.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGS. 1A-1G illustrate an embodiment of a method used to fabricate a lithographic mask provided by the invention;

FIGS. 2A-2E illustrate another embodiment of a method used to fabricate a lithographic mask provided by the invention;

FIG. 3 illustrates a method of using the lithographic mask of FIG. 1G and an etch to transfer a pattern of the mask into a resist layer;

FIG. 4 illustrates using the patterned resist layer of FIG. 3 to etch the transferred pattern into a layer of a semiconductor device;

FIG. 5 illustrates the semiconductor device of FIG. 4 after deposition of material layers over the pattern formed in FIG. 4; and

FIG. 6 illustrates an (IC) in which the semiconductor device fabricated in FIG. 6 may be incorporated or with which that device may be combined.

DETAILED DESCRIPTION

FIG. 1A illustrates an embodiment of a lithographic mask 100 at a stage of manufacture, as covered by the invention. At this stage, the mask 100 includes a mask substrate 110 and a phase shift layer 115 located over the mask substrate 110. The mask substrate 110 is translucent; that is, radiation, such as different wavelengths of light, can pass through the mask substrate 110 with a transmission sufficient to expose a photosensitive material. Non-limiting examples of radiation include white light, ultraviolet light, or monochromatic light, such as that produced by a laser. In one embodiment, the mask substrate 110 is provided. As used herein “provided or providing” includes those instances where the substrate 110 is obtained from a supplier or fabricated by the mask manufacturer itself. The substrate 110 may be a material, such as quartz, sapphire, or other material that has good transparency; that is, it has the property of transmitting light without appreciable scattering so that bodies lying beyond the substrate 110 can be seen clearly. The phase shift layer 115 is located over the mask substrate 110. The phase shift layer 115 includes a material having a desired refractive index, and a predetermined thickness of this material is locally added in order to phase shift radiation passing through a transparent portion of the mask. Phase shifting increases resolution of pattern transfer by destructive interference preventing resist exposure in the regions in which it should not be exposed.

The layer 115 may be deposited using conventional deposition processes. The layer 115 may comprise conventional lithographic mask materials. In one embodiment, the mask material may be a metallic layer, which is one that includes a metal or metal alloy, such as molybdenum. In one particular embodiment, the layer 115 is a metal silicide, such as molybdenum/silicon (MoSi). The amount of phase shift and transmission of the layer 115 may vary, depending on the type component size of the semiconductor device that is being manufactured. In certain embodiments, the polarity phase shift may be as much as 180°, but in some instances may be around 120°. In those instances where the layer 115 comprises MoSi, the transmission of the radiation through layer 115 may be about 6%. This embodiment may be applicable in larger technologies such those having node sizes of 0.5 microns or larger, which is very suitable for the manufacture of MEMS devices. In another embodiment where the layer 115 is MoSi, the transmission of the radiation through layer 115 may range between about 12% to about 40%. In this embodiment, shorter wavelengths may be employed to achieve the desired resolution. This embodiment may be applicable in smaller technologies, such as those having node sizes of about 90 nm or smaller.

In certain embodiments, a metallic mask layer 120 is deposited over the phase shift layer 115. Conventional materials and deposition processes may be used to form layer 120. For example, the metallic mask layer 120 may comprise chromium or alloys thereof. A resist layer 125 is also located over the metallic mask layer 120. The resist layer 125 may be a conventionally deposited photosensitive material, such as photoresist.

In an embodiment where the phase shift layer 115 has a lower transmission, conventional processes may be used to pattern the resist layer 125, as shown in FIG. 1B, and an etch may then be conducted through the patterned resist layer 125 to etch and pattern the mask layer 120, as shown in FIG. 1C. This may also be achieved with a conventional etch process. Following the patterning of the mask layer 120, a standard etch may be conducted to pattern the phase shift layer 115, as shown in FIG. 1D.

Following the patterning of the phase shift layer 115, the mask layer 120 is removed, which may be achieved using conventional processes. Another resist layer 130 is then deposited over the phase shift layer 115 and patterned, as shown in FIG. 1E. Conventional processes may be used to deposit and pattern the resist layer 130. As seen in FIG. 1E, the side edges of the resist layer 130 are pulled back from the side edges of the phase shift layer 115 to expose both the side edges and the top edges to provide good exposure of layer 115 to a subsequent etch.

Following the patterning of the resist layer 130, a wet etch 135 is conducted to remove those portions of the phase shift layer 115 that are not protected by the resist layer 130, as seen in FIG. 1F. The wet etch 135 etches under the resist layer 130 and causes the resist layer 130 to lift up and further expose the phase shift layer 115 to the wet etch 135. The wet etch 135 may be controlled to vary the amount of taper of the edges 115 a. For example, in one embodiment, the tapered edges can be etched to have a slope or angle 140 (as measured from the bottom edge of the phase shift layer 115) ranging from about 10° to about 75°. In one embodiment, the wet etch 135 includes using hydrogen peroxide (H₂O₂). The hydrogen peroxide may be 30% H₂O₂ by volume, and in one aspect, the H₂O₂ may be hot. In one instance, the hot H₂O₂ may have a temperature of about 55° C. The amount of time that the phase shift layer 115 is exposed to the wet etch 135 depends on the amount of desired slope. For example, the phase shift layer 135 may be exposed to the wet etch 135 for a period of time ranging from about 30 seconds to about 10 minutes. Using the wet etch 135 is beneficial because it can easily be tailored and controlled to produce tapered edges 115 a. Following the wet etch 135, the resist layer 130 is removed to arrive at the lithographic mask as seen in FIG. 1G.

Due to their graduated thickness, the tapered edges 115 a have a graded transparency to the radiation and form a gray scale mask. The lithographic mask 100 of FIG. 1G provides benefits over conventional gray scale masks because the use of this particular mask allows for improved process integration where it is desirable to use a plasma etch to etch layers that form portions of semiconductor devices. Furthermore, the tapered edges 115 a that are formed by using the lithographic mask 100 can produce a more uniform taper than conventional masks that consist of a graduated series of openings, as mentioned above. Other benefits arise in that conventional binary grey scale masks using varying densities of sub-resolution features are susceptible to patterning errors during the mask writing process. These errors include defects such as bridged and/or broken features. The conventional technology also increases mask write/fabrication time due to the increase in the number of polygon features that are patterned. In addition, conventional technology also requires extensive computer modeling to determine the correct density and dimensions for the sub-resolution features required to generate a gray scale effect at the wafer level.

FIGS. 2A-2E illustrate various stages of another method for fabricating a lithographic mask 200 in accordance with the invention. In applications involving formation of device nodes of 90 nm and below, the phase shift layer 115 may have a transmission ranging from about 12% to about 40%, as mentioned above. In addition, however, the metallic mask layer 120 may be a chromium layer that can be used with the phase shift layer 115 to obtain the appropriate amount of exposure.

FIG. 2A illustrates the mask 200 at the same stage of manufacture as illustrated in FIG. 1D, and the same steps shown in FIGS. 1A-1D can be used to arrive at the embodiment of FIG. 2A. Here, the metallic mask layer 120 has been patterned with a resist layer, and the mask layer 120 has been used to pattern the phase shift layer 115. In this particular embodiment, the mask layer 120 is shown after an etch process has been conducted such that the side edges of the mask layer 120 are set back from the side edges of the phase shift layer 115 to expose a top edges of the shift layer 115 as well, as seen in FIG. 2B. This set back should provide adequate surface area over which another resist layer 210 can be patterned the resist layer 210 is patterned such that its side edges are also set back from the side edges of the phase shift layer 115 to expose a portion of the top surface of the phase shift layer 115, as shown in FIG. 2C.

A wet etch 212, which may be the same type of wet etch as wet etch 135 discussed above regarding FIG. 1F, may be used to form tapered edges 215 a, as illustrated in FIG. 2D. Similar to wet etch 135, the wet etch 212 etches under the resist layer 210 and causes the resist layer 210 to lift up and further expose the phase shift layer 115 to the wet etch 212. The wet etch 212 may be controlled to vary the amount of taper of the edges 215 a. For example, in one embodiment, the tapered edges 215 a can be etched to have a slope or angle 240 (as measured from the bottom edge of the phase shift layer 115) ranging from about 10° to about 75.

Following the wet etch 212, the resist 210 may be conventionally removed to arrive at the lithographic mask 200, as illustrated in FIG. 2E. In this particular embodiment, the metallic layer 120 remains on the phase shift layer 115 to provide the advantages stated above. Also as mentioned above, this embodiment is particularly beneficial in those instance where very small device features are required.

FIG. 3 illustrates an embodiment of a method of using the lithographic mask 100 of FIG. 1G in the manufacture of a semiconductor device 300, which may include, for example, transistor devices, optoelectronic devices, heating elements, or microelectro-mechanical systems (MEMS). Alternatively, the lithographic mask 200 of FIG. 2E may be used instead of mask 100. The device 300 includes a substrate 310. The substrate 310 may comprise many different semiconductor materials. For example, the substrate 310 may comprise silicon, silicon-germanium, gallium arsenide, indium, phosphorous, and combinations thereof.

Located over the substrate 310 is an insulative layer 320. The insulative layer 320 electrically insulates subsequently formed layers from the substrate 310. In one embodiment, layer 320 may comprise silicon dioxide. Nevertheless, other insulative materials of varying dielectric constants might be used for layer 320. Layer 320 may have a variety of thicknesses; however, in one embodiment, it thickness may range from about 500 nm to about 1000 nm.

Located over the insulative layer 320 is a semiconductor layer 330. The layer 330, for example, may be a conductive layer or a resistive layer, such as TaAl. However, the layer 330 may also comprise TaN, TaAl(O,N), TaAlSi, TaSiC, Ti(N,O), WSi(O,N), CrSiC, TaAlN and TaAl/Ta, among others. The resistive layer 330 may also have a variety of thicknesses, however, in one embodiment, its thickness may range from about 10 nm to about 200 nm.

Another semiconductor layer 340 is located over layer 330. The layer 340, in the illustrated embodiment, may be a metal spacer layer, such as AlCu. However, in another embodiment, the layer 340 may be a dielectric layer, such as various compositions of silicon oxide or nitride, such as silicon dioxide, silicon nitride or silicon oxy-nitride. The layer 340 may additionally have a variety of thicknesses, however, in one embodiment a thickness of the layer 340 ranges from about 200 nm to about 1500 nm.

A resist layer 350, e.g., photoresist, is formed over layer 340, and as shown, has been exposed, using the lithographic mask 100 of FIG. 1G and patterned to form tapered edges 350 a. The resist layer 350 is exposed to radiation passing through the lithographic mask 100. The graded, tapered edges 115 a of the mask 100, allow varying intensities of light through to form corresponding tapered edges 350 a in the resist layer 350. As mentioned above, the gradation of the light intensity arises from the fact that the tapered edges 115 a have a variable thickness over the lateral length of the tapered edges 115 a.

Conventional processes may be used to form the layers 320, 330 and 340 on the substrate 310. For example, in one embodiment conventional microelectronic fabrication processes such as physical vapor deposition (PVD) (e.g., sputtering) or chemical vapor deposition (CVD) may be used to provide the various layers on the substrate 310. The present disclosure, however, should not be limited to any specific process for forming layers 320, 330 and 340.

With the patterned resist layer 350 in place, an etch 410 may then be conducted to etch the semiconductor layer 340 to form semiconductor layer 340 having tapered edges 340 a, as shown in FIG. 4. In one embodiment, the etch 410 may be conducted using a conventional plasma etch. Such embodiments are beneficial when it is desired to integrate the process with other plasma etching processes used to manufacture other components of the semiconductor device. The type of plasma etch will depend on the type of material that comprises the semiconductor layer 340. For example, in one embodiment, where the semiconductor layer 340 is a dielectric layer, the plasma etch may include using carbon tetrachloride as an etching gas. In another embodiment where the semiconductor layer 340 is a metallic layer, the plasma etch may include using carbon tetrafluoride, sulfur hexafluoride, or other fluorocarbon chemistries as an etching gas. Process parameters, such as flows and power settings will depend on one or more parameters, such as the material being etched, the tool, the feature size or the chemistries being used. Given the teachings herein, one skilled in the art would understand how to adjust these process parameters to conduct the etch.

FIG. 5 illustrates the semiconductor device 300 following the etch 410 of layer 340 and removal of resist layer 350 (FIG. 3). As seen in FIG. 5, with the formation of the tapered semiconductor layer 340, other semiconductor layers 510 and 520 may be deposited over layer 340. The types of layers that are deposited will depend on the type of device being constructed and the tapered edges can be used for a number of purposes, as design dictates. The device 100, as mentioned above, may be a number of electrical devices, such as an optoelectronics device, fuses, diodes, heating element, or MEMS device, which would also include transistors used to control such devices.

FIG. 6 illustrates the semiconductor device configured as an integrated circuit (IC) 600. The device 600 includes transistor devices 620 located over/in a substrate 610. The transistor devices 620 in this embodiment each include a gate structure 630 and source/drain regions 640. Since the feature in FIG. 5 may be incorporated into IC 600 in a number of ways, its incorporation in FIG. 6 is not specifically illustrated. However, those who are skilled in the art would understand how to incorporate the feature of FIG. 5 as required by design. For example, the feature of FIG. 5 may be configured as a capacitor, resistor, fuse, Schottky diode, or heating element, etc. without departing from the scope of this disclosure and combined with or incorporated into the IC 600. Located over the devices 620 are interconnects 660 located within dielectric layers 670. As illustrated, the interconnects 660 may electrically contact one or more of the transistor devices 620.

Those skilled in the art will appreciate that other and further additions, deletions, substitutions, and modifications may be made to the described embodiments without departing from the scope the disclosure set forth herein. 

1. A method of manufacturing a semiconductor device comprising: placing a mask layer over a layer, the layer located over a semiconductor substrate; using a lithographic mask to expose the mask layer located over a semiconductor substrate, the lithographic mask including a mask substrate having a metallic layer located thereover, the metallic layer having tapered edges wherein the tapered edges have a graded translucency; patterning the mask layer including forming tapered edges on the mask layer; and etching the layer through the patterned mask layer to form a layer having tapered edges.
 2. The method of claim 1 further including, forming gate electrodes over the semiconductor substrate; forming source/drain adjacent the semiconductor substrate; forming dielectric layers over the gate electrodes; and forming interconnects over and within the dielectric layers.
 3. The method of claim 1 wherein etching the layer includes etching a metallic layer.
 4. The method of claim 1 wherein etching includes using a plasma etch.
 5. The method of claim 4 wherein the layer is a dielectric layer and the plasma etch includes using carbon tetrachloride as an etching gas.
 6. The method of claim 4 wherein the layer is a metallic layer and the plasma etch includes using carbon tetrafluoride or sulfur hexafluoride as an etching gas.
 7. A gray scale lithographic mask, comprising: a transparent substrate; and a metallic layer located over the substrate, wherein the metallic layer has tapered edges with a graded transparency.
 8. The mask of claim 7, wherein the transparent substrate is quartz.
 9. The mask of claim 7, wherein the metallic layer is a molybdenum silicon layer.
 10. The mask of claim 9, wherein the molybdenum silicon layer has a transmission of about 6%.
 11. The mask of claim 7, wherein the molybdenum silicon layer has a transmission ranging from about 12% to about 40%.
 12. The mask of claim 7, wherein the tapered edges have a slope equal to or less than about 75°.
 13. A method of fabricating a gray scale lithographic mask, comprising: providing a transparent substrate; placing a metallic layer over the transparent substrate; forming a patterned etch mask over the metallic layer to expose portions of the metallic layer; and etching the exposed portions of the metallic layer to form tapered edges on the metallic layer, the tapered edges having a graded transparency.
 14. The method of in claim 13, wherein placing the metallic layer includes placing a molybdenum silicon layer on the transparent substrate.
 15. The method of claim 14, wherein the metallic layer has a transmission of about 6%.
 16. The method of claim 15, wherein the metallic layer is a first metallic layer and forming a patterned etch mask includes: patterning a second metallic layer with a first resist; removing the first resist to form an etch mask with the second metallic layer; patterning the first metallic layer using the second metallic layer as an etch mask; removing the second metallic layer; and placing a second resist over the patterned first metallic layer such that side edges of the second resist are set back from side edges of the first metallic layer.
 17. The method of claim 16, wherein the second metallic layer is chromium.
 18. The method of claim 14, wherein the metallic layer has a transmission ranging from about 12% to about 40%.
 19. The method of claim 18, wherein the metallic layer is a first metallic layer and forming a patterned etch mask includes: patterning a second metallic layer with a first resist such that side edges of the second metallic layer are set back from side edges of the first metallic layer; removing the first resist; and placing a second resist on the patterned second metallic layer wherein the second resist overlaps the side edges of the second metallic layer and side edges of the second resist are set back from the side edges of the first metallic layer.
 20. The method of claim 13, wherein etching the metallic layer is conducted with a wet etch.
 21. The method of claim 22, wherein the wet etch includes using hydrogen peroxide.
 22. The method of claim 22, wherein a temperature of the hydrogen peroxide during the etch is about 55° C.
 23. The method of claim 22, wherein the wet etch is conducted for a period of time ranging from about 30 seconds to about 10 minutes. 